Brake disc for a vehicle disc brake

ABSTRACT

Brake disc for a vehicle disc brake, comprising a radially inner hub portion ( 1   a ) intended to be non-rotatably joined to a wheel hub and a surrounding, radially outer disc portion with oppositely facing friction surfaces. The outer disc portion is formed of two disc elements ( 4 ) joined to the hub portion, which are separated by spacers ( 7   a–   7   d ), which define passages for cooling air.

BACKGROUND OF THE INVENTION

The present invention relates to a brake disc for a vehicle disc brake,comprising a radially inner hub portion intended to be non-rotatablyjoined to a wheel hub, a surrounding, radially outer disc portion withfriction surfaces facing in opposite directions, and passages disposedin the outer disc portion, said passages being arranged to guide coolingair in the disc material between the friction surfaces.

DESCRIPTION OF THE RELATED ART

So-called ventilated brake discs, which are made to increase the coolingeffect of the ambient air by diverting heat generated during braking,occur in two principle types. One type has channels which extendradially through the disc from the inner periphery of the hub to theouter periphery of the surrounding disc portion. The channels thus haveinlet openings in the inner periphery and outlet openings in the outerperiphery. As the disc rotates, a guided airflow is created through thechannels from the inlet to the outlet. The other type of ventilatedbrake disc consists of two disc elements, which are fixed to a hub andto each other side-by-side with an intermediate space created by aplurality of spacers in the form of pillars.

By ventilating the disc, the mean temperature of the disc is reduced.Since the wear on the disc and pads is strongly dependent ontemperature, a reduction in temperature will have a positive effect onthis wear. Furthermore, the highest temperature of the disc is reducedfor most driving styles, which in turn reduces the risk of brake fadeand the risk of cracking. One disadvantage of having channels openinginto the inner periphery of the hub is, however, that the material massis reduced in that portion of the brake disc where the stresses aregreatest, both as regards braking force and temperature difference. Thehigh stresses in connection with the holes in the hub increase the riskof cracking.

SUMMARY OF THE INVENTION

The purpose of the present invention is to achieve a brake disc of thetype described by way of introduction, which is constructed so thatsatisfactory cooling can be achieved without sacrificing strength in thedisc hub.

This is achieved according to the invention by virtue of the fact thatthe passages have inlets and outlets for cooling air at or in thevicinity of the periphery of the radially outer disc portion and thatsaid passages do not penetrate into the hub portion.

The invention is based, in one embodiment, on the above described pillardesign for a brake disc, but instead of arranging pillars in the hubportion as well, so that air can circulate through the entire disc fromits inner periphery to its outer periphery, the disc is made with a hubportion which is not penetrated into by the air passages. In combinationwith certain designs of the vehicle wheel house, it has been shown thatsatisfactory cooling can be achieved without cooling air channelsthrough the hub.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where

FIG. 1 shows an end view of a first embodiment of a brake disc accordingto the invention,

FIG. 2 shows a cross-section along the line II—II in FIG. 1,

FIG. 3 shows a longitudinal section along the line III—III in FIG. 4through a second embodiment of a brake disc according to the invention,and

FIG. 4 shows a cross-section along the line IV—IV in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The brake disc 1 shown in FIGS. 1 and 2 has a radially inner hub portion1 a, the inner lateral surface of which is provided with splines 2, 3intended to engage corresponding splines in a wheel hub (not shown).Examples of such non-rotatable fixation of the brake disc 1, as analternative to a more conventional fixation whereby a holed fixingflange on the brake disc is screwed securely to a flange on the wheelhub, are shown and described in SE-A-502 189. The hub portion 1 a iscast in one piece with a pair of disc elements 4 arranged with anintermediate spacing. The disc element surfaces 5 facing away from eachother form the friction surfaces of the brake disc, against which brakepads (not shown) are pressed during braking. In the intermediate space 7between the disc elements 4, there are spacer elements 7 a, 7 b, 7 c and7 d. The spacer elements 7 a–7 d define passages 8 and 9 between them,through which air flows when the brake disc rotates.

The embodiment shown in FIGS. 3 and 4 of the brake disc 1 differs fromthat described above only in that it has a more conventional hub portion1 b, which has a flange 14 provided with holes 13 for securely screwingto a flange on a wheel hub.

The invention achieves cooling of the brake disc without channelspenetrating into the hub portion. This reduces the stresses as comparedwith known designs with radial channels through the hub portion.

1. Brake disc for a vehicle disc brake, comprising a radially inner hubportion (1 a) intended to be non-rotatably joined to a wheel hub, asurrounding, radially outer disc portion (4) with oppositely facingfriction surfaces (5), and passages (8, 9) disposed in the outer discportion, said passages being arranged to guide cooling air in a discmaterial between the friction surfaces, characterized in that all thepassages (8, 9) have inlets and outlets for cooling air at a radiallyoutermost periphery of the outer disc portion, and that said passages donot penetrate into the hub portion, and in that the outer disc portionis formed by two disc elements (4) joined to the hub portion, said discelements being separated by a plurality of individual, circumferentiallyspaced apart spacer elements (7 a–7 d), which define said passages (8,9) extending between adjacent spacer elements, wherein the spacerelements are in the form of plural concentric rows of pillars, and thepassage inlets are remote from a radially inner periphery of the outerdisc portion.
 2. Brake disc according to claim 1, characterized in thatthe hub portion (1 a) has an inner periphery, which is provided withsplines (2) intended to engage corresponding splines on the wheel hub.3. Brake disc according to claim 1, characterized in that the hubportion (1 b) is made with a flange (14) provided with borings (13) forscrewing it securely to a fixing flange on a wheel hub.
 4. Brake discfor a vehicle disc brake, comprising a radially inner hub portion (1 a)intended to be non-rotatably joined to a wheel hub, a surrounding,radially outer disc portion (4) with oppositely facing friction surfaces(5), and passages (8, 9) disposed in the outer disc portion, saidpassages being arranged to guide cooling air in a disc material betweenthe friction surfaces, characterized in that all the passages (8, 9)have inlets and outlets for cooling air only at a radially outermostperiphery of the outer disc portion, and that said passages do notpenetrate into the hub portion, and in that the outer disc portion isformed by two disc elements (4) joined to the hub portion, said discelements being separated by a plurality of individual, circumferentiallyspaced apart spacer elements (7 a–7 d), which define said passages (8,9) extending between adjacent spacer elements, wherein the spacerelements are in the form of plural concentric rows of pillars, and thepassage inlets are remote from a radially inner periphery of the outerdisc portion.
 5. Brake disc according to claim 4, characterized in thatthe hub portion (1 a) has an inner periphery, which is provided withsplines (2) intended to engage corresponding splines on the wheel hub.6. Brake disc according to claim 4, characterized in that the hubportion (1 b) is made with a flange (14) provided with borings (13) forscrewing it securely to a fixing flange on a wheel hub.